Another, called Psionic Assault, provides you with a few specialized Protoss units and tests how long you are able to survive against waves of enemies. Rush Defense teaches players to withstand an early Zerg rush, while Infestation teaches you to use stealthy Zerg units as effectively as possible.

Each challenge mode is given a level of difficulty – basic, advanced or expert – and each has a tiered goal system – lasting through 60 zerg units in Rush Defense, for example, might net you a bronze medal, while lasting through 150 could snag you a gold. We're not sure if medals do anything special, but we suspect they'll be tied to the achievement system.

At some point after Wings of Liberty (which is to say, when it is ready), Blizzard will release the second episode, Heart of the Swarm, which will follow the events of the Zerg and the Zergified Sarah Kerrigan. And after that (possibly around the year 2067) the Protoss episode, Legacy of the Void, will continue the saga centered on Zeratul, a Protoss Dark Templar.

The MULE is a new harvesting unit. Whereas the SCVs can harvest as well as repair and build, the MULEs can just harvest. They can hold three times more minerals than SCVs, but have a limited lifespan and will, left to their own devices, eventually expire.

The Hellion, a four-wheeled flame-throwing buggy, replaces that crummy old missile-launching Vulture Hoverbike. Despite the bizarre technological backstep, Hellions provide an important link in terms of balance. In the original StarCraft, Firebats (rather slow-moving flame-throwing infantry) were used for tearing down infantry swarms and constructs, but moving slower than other infantry made them pretty useless in most combat situations. The speedy Hellions now fix that little problem.

Medivacs are card-carrying members of the consolidation club, too, replacing both the medic (from Brood War) and the dropship (from vanilla StarCraft). Capable of ferrying ground units across the map, and of healing infantry units, the Medivac is likely to become a central unit for most strategies.

Reapers are awesome. Reapers are so awesome. If the movie The Rocketeer starred Bruce Willis in his Die Hard 3 era, and was directed by John Woo, you'd get something about half as badass as a Reaper. That said, you could just look at Dawn of War's Tactical Marines and get something pretty much identical. Reapers are dual-pistol-wielding jetpack-wearing light infantry. They're fast, relatively cheap, and best of all, can traverse cliffs, making them one of the most mobile and flexible units in the game. And they look spiffy.

Though maybe not as spiffy as a Thor. Essentially the battle cruiser of ground units, Thors are hulking, armored, killing machines. With four anti-air guns mounted on its back, and two particle-accelerator cannons for dealing with punks on the land, Thors have no discernable weakness, beyond the huge amount of time and resources required to climb the tech-tree high enough to produce them, and then the (slightly less) huge amount of resources required to actually make one.

Marauders are like less-awesome Reapers. Sure, they're bigger, and sure, they can fire concussion missiles that slow ground units down, and sure, they tear armored units to shreds, but can they fly up cliffs? No? Pfft, whatever.

The Banshee is a thing to be feared. A very powerful air-to-ground unit, the banshee is capable of blowing through almost anything with legs or wheels. Oh, and it can cloak. Its only truly reliable counter are flying anti-air units like the Corruptor or the Phoenix.

The Raven is similar to the science vessel from the original and is incapable of any standard attack. Instead, it's a detector, so burrowed or cloaked units can't hide. It can lay down auto-turrets (with no set lifespan) for a fairly small energy cost, and can drop "hunter-seeker missiles," floating bombs that track the movement of a single enemy, kill it on contact, and deal severe damage to any foes unlucky enough to be nearby. The only way to avoid the missile, in fact, is to run far, far away, making it a very impressive tactical weapon.

You may remember the Viking from a little-known 1980s cartoon called Transformers, when it was called Starscream. Yes, the Viking is a robot that can transform into a plane. Unlike Starscream, though, the Viking is much more effective as an aircraft than a crummy ground unit. It's a purpose-built anti-air aircraft; it just also happens to be a robot that can occasionally help on the ground, too.